Method for receiving downlink control channel by MTC device, and terminal

ABSTRACT

An embodiment of the present specification provides a method for receiving a downlink control channel by a machine type communication (MTC) device. The method comprises: a step of receiving, by the downlink control channel, setting information about the maximum number of physical resource blocks (PRBs) which can be transmitted by a base station; a step of receiving, by the MTC device, setting information about a set of control channel monitoring PRBs which should monitor the downlink control channel; and a step of monitoring the downlink control channel on the PRBs according to the setting information about the set of control channel monitoring PRBs, wherein if the number of sets of control channel monitoring PRBs exceeds the maximum number of PRBs, the downlink control channel may be monitored only on the sets of PRBs equal to or less than the maximum number of PRBs.

This application is a continuation of U.S. patent application Ser. No.15/120,490, filed Aug. 19, 2016, which is a National Stage Applicationof International Application No. PCT/KR2015/002263, filed Mar. 10, 2015and claims the benefit of U.S. Provisional Application No. 61/954,622,filed Mar. 18, 2014, all of which are incorporated by reference in theirentirety herein.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to mobile communication.

Related Art

3^(rd) generation partnership project (3GPP) long term evolution (LTE)evolved from a universal mobile telecommunications system (UMTS) isintroduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequencydivision multiple access (OFDMA) in a downlink, and uses singlecarrier-frequency division multiple access (SC-FDMA) in an uplink. The3GPP LTE employs multiple input multiple output (MIMO) having up to fourantennas. In recent years, there is an ongoing discussion on 3GPPLTE-advanced (LTE-A) evolved from the 3GPP LTE.

As disclosed in 3GPP TS 36.211 V10.4.0 (2011-12) “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 10)”, 3GPP LTE/LTE-A may divide the physical channel into adownlink channel, i.e., a physical downlink shared channel (PDSCH) and aphysical downlink control channel (PDCCH), and an uplink channel, i.e.,a physical uplink shared channel (PUSCH) and a physical uplink controlchannel (PUCCH).

Meanwhile, in recent years, research into communication between devicesor the device and a server without human interaction, that is, withouthuman intervention, that is, machine-type communication (MTC) has beenactively conducted. The MTC represents a concept in which not a terminalused by human but a machine performs communication by using the existingwireless communication network.

Since MTC has features different from communication of a normal UE, aservice optimized to MTC may differ from a service optimized tohuman-to-human communication. In comparison with a current mobilenetwork communication service, MTC can be characterized as a differentmarket scenario, data communication, less costs and efforts, apotentially great number of MTC devices, wide service areas, low trafficfor each MTC device, etc.

Meanwhile, it is recently suggested to restrict a bandwidth for adownlink channel for low-cost or low-complexity MTC devices.

In this case, the MTC devices may have difficulty in receiving adownlink channel on a restricted bandwidth.

SUMMARY OF THE INVENTION

Accordingly, the disclosure of the specification has been made in aneffort to solve the problem.

To achieve the foregoing aspect, a method according to the disclosure ofthe present specification is a method for a machine-type communication(MTC) device to receive a downlink control channel, the methodincluding: receiving configuration information on a maximum number ofphysical resource blocks (PRBs) which are available for a base stationto transmit the downlink control channel; receiving configurationinformation on a set of PRBs for monitoring control channel in which theMTC device needs to monitor the downlink control channel; and monitoringthe downlink control channel on the PRBs according to the configurationinformation on the set of PRBs for monitoring control channel, whereinwhen a number of the PRBs based on the set of PRBs for monitoringcontrol channel exceeds the maximum number of PRBs, the downlink controlchannel may be monitored only on a set of a number of PRBs equal to orless than the maximum number of PRBs.

Here, the maximum number of PRBs for the downlink control channel may be6.

Further, the downlink control channel may be monitored only on a set ofa number of PRBs having a relatively low PRB index, equal to or lessthan the maximum number of PRBs, in the set of PRBs for monitoringcontrol channel.

Further, the MTC device may assume that PRBs in which the downlinkcontrol channel is not monitored in the set of PRBs for monitoringcontrol channel are punctured or rate-matched.

Further, the set of PRBs for monitoring control channel may be setindependently of a set of data channel monitoring PRBs in which the MTCdevice needs to monitor a downlink data channel.

Further, the set of PRBs for monitoring control channel may be set thesame as a set of data channel monitoring PRBs in which the MTC deviceneeds to monitor a downlink data channel.

Further, the maximum number of PRBs for the downlink control channel maybe set independently of a maximum number of PRBs which are available forthe base station to transmit a downlink data channel.

Further, the maximum number of PRBs for the downlink control channel maybe set such that a sum of the maximum number of PRBs for the downlinkcontrol channel and a maximum number of PRBs which are available for thebase station to transmit a downlink data channel is a reference PRBnumber.

Here, the reference PRB number may be 6.

Further, the downlink control channel may be an enhanced physicaldownlink control channel (EPDCCH), and the downlink data channel may bea physical downlink shared channel (PDSCH).

To achieve the foregoing aspect, a UE according to the disclosure of thepresent specification is an MTC device for receiving a downlink controlchannel, the MTC device including a radio frequency (RF) unit to receiveconfiguration information on a maximum number of PRBs which areavailable for a base station to transmit the downlink control channeland configuration information on a set of PRBs for monitoring controlchannel in which the MTC device needs to monitor the downlink controlchannel; and a processor to monitor the downlink control channel on thePRBs according to the configuration information on the set of PRBs formonitoring control channel, wherein when a number of the PRBs based onthe set of PRBs for monitoring control channel exceeds the maximumnumber of PRBs, the processor may monitor the downlink control channelonly on a set of a number of PRBs equal to or less than the maximumnumber of PRBs.

According to the disclosure of the present specification, the foregoingproblem of the conventional technology. More specifically, according tothe disclosure of the present specification, a low-cost orlow-complexity MTC device may efficiently receive a downlink controlchannel on a restricted bandwidth.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless communication system.

FIG. 2 illustrates a structure of a radio frame according to frequencydivision duplex (FDD) of 3rd generation partnership project (3GPP) longterm evolution (LTE).

FIG. 3 illustrates a structure of a downlink radio frame according totime division duplex (TDD) in 3GPP LTE.

FIG. 4 illustrates an example of a resource grid for one uplink ordownlink slot in 3GPP LTE.

FIG. 5 illustrates a structure of a downlink subframe.

FIG. 6 illustrates an example of resource mapping of a physical downlinkcontrol channel (PDCCH).

FIG. 7 illustrates an example of monitoring of a PDCCH.

FIG. 8 illustrates the architecture of a UL subframe in 3GPP LTE.

FIG. 9 illustrates a subframe having an enhanced PDCCH (EPDCCH).

FIG. 10 illustrates an example of a physical resource block (PRB) pair.

FIG. 11a illustrates an example of machine-type communication (MTC).

FIG. 11b illustrates an example of cell coverage extension for an MTCdevice.

FIG. 12 illustrates an example of a PDSCH monitoring PRB region for anMTC device.

FIG. 13 illustrates an example of cross subframe scheduling for an MTCdevice.

FIG. 14 is a block diagram illustrating a wireless communication systemaccording to the disclosure of the present specification.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, based on 3rd Generation Partnership Project (3GPP) longterm evolution (LTE) or 3GPP LTE-advanced (LTE-A), the present inventionwill be applied. This is just an example, and the present invention maybe applied to various wireless communication systems. Hereinafter, LTEincludes LTE and/or LTE-A.

The technical terms used herein are used to merely describe specificembodiments and should not be construed as limiting the presentinvention. Further, the technical terms used herein should be, unlessdefined otherwise, interpreted as having meanings generally understoodby those skilled in the art but not too broadly or too narrowly.Further, the technical terms used herein, which are determined not toexactly represent the spirit of the invention, should be replaced by orunderstood by such technical terms as being able to be exactlyunderstood by those skilled in the art. Further, the general terms usedherein should be interpreted in the context as defined in thedictionary, but not in an excessively narrowed manner.

The expression of the singular number in the present invention includesthe meaning of the plural number unless the meaning of the singularnumber is definitely different from that of the plural number in thecontext. In the following description, the term ‘include’ or ‘have’ mayrepresent the existence of a feature, a number, a step, an operation, acomponent, a part or the combination thereof described in the presentinvention, and may not exclude the existence or addition of anotherfeature, another number, another step, another operation, anothercomponent, another part or the combination thereof.

The terms ‘first’ and ‘second’ are used for the purpose of explanationabout various components, and the components are not limited to theterms ‘first’ and ‘second’. The terms ‘first’ and ‘second’ are only usedto distinguish one component from another component. For example, afirst component may be named as a second component without deviatingfrom the scope of the present invention.

It will be understood that when an element or layer is referred to asbeing “connected to” or “coupled to” another element or layer, it can bedirectly connected or coupled to the other element or layer orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly connected to” or “directlycoupled to” another element or layer, there are no intervening elementsor layers present.

Hereinafter, exemplary embodiments of the present invention will bedescribed in greater detail with reference to the accompanying drawings.In describing the present invention, for ease of understanding, the samereference numerals are used to denote the same components throughout thedrawings, and repetitive description on the same components will beomitted. Detailed description on well-known arts which are determined tomake the gist of the invention unclear will be omitted. The accompanyingdrawings are provided to merely make the spirit of the invention readilyunderstood, but not should be intended to be limiting of the invention.It should be understood that the spirit of the invention may be expandedto its modifications, replacements or equivalents in addition to what isshown in the drawings.

As used herein, ‘base station’ generally refers to a fixed station thatcommunicates with a wireless device and may be denoted by other termssuch as eNB (evolved-NodeB), BTS (base transceiver system), or accesspoint.

As used herein, ‘user equipment (UE)’ may be stationary or mobile, andmay be denoted by other terms such as device, wireless device, terminal,MS (mobile station), UT (user terminal), SS (subscriber station), MT(mobile terminal) and etc.

FIG. 1 illustrates a wireless communication system.

As seen with reference to FIG. 1, the wireless communication systemincludes at least one base station (BS) 20. Each base station 20provides a communication service to specific geographical areas(generally, referred to as cells) 20 a, 20 b, and 20 c. The cell can befurther divided into a plurality of areas (sectors).

The UE generally belongs to one cell and the cell to which the UE belongis referred to as a serving cell. A base station that provides thecommunication service to the serving cell is referred to as a servingBS. Since the wireless communication system is a cellular system,another cell that neighbors to the serving cell is present. Another cellwhich neighbors to the serving cell is referred to a neighbor cell. Abase station that provides the communication service to the neighborcell is referred to as a neighbor BS. The serving cell and the neighborcell are relatively decided based on the UE.

Hereinafter, a downlink means communication from the base station 20 tothe UE1 10 and an uplink means communication from the UE 10 to the basestation 20. In the downlink, a transmitter may be a part of the basestation 20 and a receiver may be a part of the UE 10. In the uplink, thetransmitter may be a part of the UE 10 and the receiver may be a part ofthe base station 20.

Meanwhile, the wireless communication system may be generally dividedinto a frequency division duplex (FDD) type and a time division duplex(TDD) type. According to the FDD type, uplink transmission and downlinktransmission are achieved while occupying different frequency bands.According to the TDD type, the uplink transmission and the downlinktransmission are achieved at different time while occupying the samefrequency band. A channel response of the TDD type is substantiallyreciprocal. This means that a downlink channel response and an uplinkchannel response are approximately the same as each other in a givenfrequency area. Accordingly, in the TDD based wireless communicationsystem, the downlink channel response may be acquired from the uplinkchannel response. In the TDD type, since an entire frequency band istime-divided in the uplink transmission and the downlink transmission,the downlink transmission by the base station and the uplinktransmission by the terminal may not be performed simultaneously. In theTDD system in which the uplink transmission and the downlinktransmission are divided by the unit of a subframe, the uplinktransmission and the downlink transmission are performed in differentsubframes.

Hereinafter, the LTE system will be described in detail.

FIG. 2 illustrates a structure of a radio frame according to FDD of 3rdgeneration partnership project (3GPP) long term evolution (LTE).

The radio frame of FIG. 2 may be found in the section 5 of 3GPP TS36.211 V10.4.0 (2011-12) “Evolved Universal Terrestrial Radio Access(E-UTRA); Physical Channels and Modulation (Release 10)”.

The radio frame includes 10 subframes indexed 0 to 9. One subframeincludes two consecutive slots. Accordingly, the radio frame includes 20slots. The time taken for one subframe to be transmitted is denoted TTI(transmission time interval). For example, the length of one subframemay be 1 ms, and the length of one slot may be 0.5 ms.

The structure of the radio frame is for exemplary purposes only, andthus the number of subframes included in the radio frame or the numberof slots included in the subframe may change variously.

Meanwhile, one slot may include a plurality of OFDM symbols. The numberof OFDM symbols included in one slot may vary depending on a cyclicprefix (CP).

FIG. 3 illustrates a structure of a downlink radio frame according toTDD in 3GPP LTE.

For this, 3GPP TS 36.211 V10.4.0 (2011-23) “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)”, Ch. 4 may be referenced, and this is for TDD (timedivision duplex).

Subframes having index #1 and index #6 are denoted special subframes,and include a DwPTS (Downlink Pilot Time Slot: DwPTS), a GP (GuardPeriod) and an UpPTS (Uplink Pilot Time Slot). The DwPTS is used forinitial cell search, synchronization, or channel estimation in aterminal. The UpPTS is used for channel estimation in the base stationand for establishing uplink transmission sync of the terminal. The GP isa period for removing interference that arises on uplink due to amulti-path delay of a downlink signal between uplink and downlink.

In TDD, a DL (downlink) subframe and a UL (Uplink) co-exist in one radioframe. Table 1 shows an example of configuration of a radio frame.

TABLE 1 Switch- UL-DL point Subframe index configuration periodicity 0 12 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5 ms D S U U D D S U U D 25 ms D S U D D D S U D D 3 10 ms  D S U U U D D D D D 4 10 ms  D S U U DD D D D D 5 10 ms  D S U D D D D D D D 6 5 ms D S U U U D S U U D

‘D’ denotes a DL subframe, ‘U’ a UL subframe, and ‘S’ a specialsubframe. When receiving a UL-DL configuration from the base station,the terminal may be aware of whether a subframe is a DL subframe or a ULsubframe according to the configuration of the radio frame.

FIG. 4 illustrates an example of a resource grid for one uplink ordownlink slot in 3GPP LTE.

Referring to FIG. 4, the uplink slot includes a plurality of OFDM(orthogonal frequency division multiplexing) symbols in the time domainand NRB resource blocks (RB s) in the frequency domain. For example, inthe LTE system, the number of resource blocks (RBs), i.e., NRB, may beone from 6 to 110.

The resource block is a unit of resource allocation and includes aplurality of sub-carriers in the frequency domain. For example, if oneslot includes seven OFDM symbols in the time domain and the resourceblock includes 12 sub-carriers in the frequency domain, one resourceblock may include 7×12 resource elements (REs).

FIG. 5 illustrates a structure of a downlink subframe.

In FIG. 5, assuming the normal CP, one slot includes seven OFDM symbols,by way of example.

The DL (downlink) subframe is split into a control region and a dataregion in the time domain. The control region includes up to first threeOFDM symbols in the first slot of the subframe. However, the number ofOFDM symbols included in the control region may be changed. A PDCCH(physical downlink control channel) and other control channels areassigned to the control region, and a PDSCH is assigned to the dataregion.

The physical channels in 3GPP LTE may be classified into data channelssuch as PDSCH (physical downlink shared channel) and PUSCH (physicaluplink shared channel) and control channels such as PDCCH (physicaldownlink control channel), PCFICH (physical control format indicatorchannel), PHICH (physical hybrid-ARQ indicator channel) and PUCCH(physical uplink control channel).

The PCFICH transmitted in the first OFDM symbol of the subframe carriesCIF (control format indicator) regarding the number (i.e., size of thecontrol region) of OFDM symbols used for transmission of controlchannels in the subframe. The wireless device first receives the CIF onthe PCFICH and then monitors the PDCCH.

Unlike the PDCCH, the PCFICH is transmitted through a fixed PCFICHresource in the subframe without using blind decoding.

The PHICH carries an ACK (positive-acknowledgement)/NACK(negative-acknowledgement) signal for a UL HARQ (hybrid automatic repeatrequest). The ACK/NACK signal for UL (uplink) data on the PUSCHtransmitted by the wireless device is sent on the PHICH.

The PBCH (physical broadcast channel) is transmitted in the first fourOFDM symbols in the second slot of the first subframe of the radioframe. The PBCH carries system information necessary for the wirelessdevice to communicate with the base station, and the system informationtransmitted through the PBCH is denoted MIB (master information block).In comparison, system information transmitted on the PDSCH indicated bythe PDCCH is denoted SIB (system information block).

The PDCCH may carry activation of VoIP (voice over internet protocol)and a set of transmission power control commands for individual UEs insome UE group, resource allocation of an upper layer control messagesuch as a random access response transmitted on the PDSCH, systeminformation on DL-SCH, paging information on PCH, resource allocationinformation of UL-SCH (uplink shared channel), and resource allocationand transmission format of DL-SCH (downlink-shared channel). A pluralityof PDCCHs may be sent in the control region, and the terminal maymonitor the plurality of PDCCHs. The PDCCH is transmitted on one CCE(control channel element) or aggregation of some consecutive CCEs. TheCCE is a logical allocation unit used for providing a coding rate perradio channel's state to the PDCCH. The CCE corresponds to a pluralityof resource element groups. Depending on the relationship between thenumber of CCEs and coding rates provided by the CCEs, the format of thePDCCH and the possible number of PDCCHs are determined.

The control information transmitted through the PDCCH is denoteddownlink control information (DCI). The DCI may include resourceallocation of PDSCH (this is also referred to as DL (downlink) grant),resource allocation of PUSCH (this is also referred to as UL (uplink)grant), a set of transmission power control commands for individual UEsin some UE group, and/or activation of VoIP (Voice over InternetProtocol).

The base station determines a PDCCH format according to the DCI to besent to the terminal and adds a CRC (cyclic redundancy check) to controlinformation. The CRC is masked with a unique identifier (RNTI; radionetwork temporary identifier) depending on the owner or purpose of thePDCCH. In case the PDCCH is for a specific terminal, the terminal'sunique identifier, such as C-RNTI (cell-RNTI), may be masked to the CRC.Or, if the PDCCH is for a paging message, a paging indicator, forexample, P-RNTI (paging-RNTI) may be masked to the CRC. If the PDCCH isfor a system information block (SIB), a system information identifier,SI-RNTI (system information-RNTI), may be masked to the CRC. In order toindicate a random access response that is a response to the terminal'stransmission of a random access preamble, an RA-RNTI (randomaccess-RNTI) may be masked to the CRC.

In 3GPP LTE, blind decoding is used for detecting a PDCCH. The blinddecoding is a scheme of identifying whether a PDCCH is its own controlchannel by demasking a desired identifier to the CRC (cyclic redundancycheck) of a received PDCCH (this is referred to as candidate PDCCH) andchecking a CRC error. The base station determines a PDCCH formataccording to the DCI to be sent to the wireless device, then adds a CRCto the DCI, and masks a unique identifier (this is referred to as RNTI(radio network temporary identifier) to the CRC depending on the owneror purpose of the PDCCH.

FIG. 6 illustrates an example of resource mapping of a PDCCH.

R0 denotes a reference signal of a 1^(st) antenna, R1 denotes areference signal of a 2^(nd) antenna, R2 denotes a reference signal of a3^(rd) antenna, and R3 denotes a reference signal of a 4^(th) antenna.

A control region in a subframe includes a plurality of control channelelements (CCEs). The CCE is a logical allocation unit used to providethe PDCCH with a coding rate depending on a state of a radio channel,and corresponds to a plurality of resource element groups (REGs). TheREG includes a plurality of resource elements (REs). According to therelationship between the number of CCEs and the coding rate provided bythe CCEs, a PDCCH format and a possible PDCCH bit number are determined.

A BS determines the number of CCEs used in transmission of the PDCCHaccording to a channel state. For example, a UE having a good DL channelstate may use one CCE in PDCCH transmission. A UE having a poor DLchannel state may use 8 CCEs in PDCCH transmission.

One REG (indicated by a quadruplet in the drawing) includes 4 REs. OneCCE includes 9 REGs. The number of CCEs used to configure one PDCCH maybe selected from {1, 2, 4, 8}. Each element of {1, 2, 4, 8} is referredto as a CCE aggregation level.

A control channel consisting of one or more CCEs performs interleavingin unit of REG, and is mapped to a physical resource after performingcyclic shift based on a cell identifier (ID).

FIG. 7 illustrates an example of monitoring of a PDCCH.

A UE cannot know about a specific position in a control region in whichits PDCCH is transmitted and about a specific CCE aggregation or DCIformat used for transmission. A plurality of PDCCHs can be transmittedin one subframe, and thus the UE monitors the plurality of PDCCHs inevery subframe. Herein, monitoring is an operation of attempting PDCCHdecoding by the UE according to a PDCCH format.

The 3GPP LTE uses a search space to reduce an overhead of blinddecoding. The search space can also be called a monitoring set of a CCEfor the PDCCH. The UE monitors the PDCCH in the search space.

The search space is classified into a common search space and aUE-specific search space. The common search space is a space forsearching for a PDCCH having common control information and consists of16 CCEs indexed with 0 to 15. The common search space supports a PDCCHhaving a CCE aggregation level of {4, 8}. However, a PDCCH (e.g., DCIformats 0, 1A) for carrying UE-specific information can also betransmitted in the common search space. The UE-specific search spacesupports a PDCCH having a CCE aggregation level of {1, 2, 4, 8}.

Table 2 below shows the number of PDCCH candidates monitored by awireless device.

TABLE 2 Search space S^((L)) _(k) Number M^((L)) of Aggregation SizePDCCH Type level L [in CCEs] candidates UE- 1 6 6 specific 2 12 6 4 8 28 16 2 Common 4 16 4 8 16 2

A size of the search space is determined by Table 2 above, and a startpoint of the search space is defined differently in the common searchspace and the UE-specific search space. Although a start point of thecommon search space is fixed irrespective of a subframe, a start pointof the UE-specific search space may vary in every subframe according toa UE identifier (e.g., C-RNTI), a CCE aggregation level, and/or a slotnumber in a radio frame. If the start point of the UE-specific searchspace exists in the common search space, the UE-specific search spaceand the common search space may overlap with each other.

In a CCE aggregation level L∈{1, 2, 3, 4}, a search space S^((L)) _(k)is defined as a set of PDCCH candidates. A CCE corresponding to a PDCCHcandidate m of the search space S^((L)) _(k) is given by Equation 1below.L{(Y _(k) +m′)mod └N _(CCE,k) /L┘}+i  [Equation 1]

Herein, i=0, 1, . . . , L−1, m=0, . . . , M^((L))−1, and N_(CCE,k)denotes the total number of CCEs that can be used for PDCCH transmissionin a control region of a subframe k. The control region includes a setof CCEs numbered from 0 to N_(CCE,k)−1. M^((L)) denotes the number ofPDCCH candidates in a CCE aggregation level L of a given search space.

If a carrier indicator field (CIF) is configured for the wirelessdevice, m′=m+M^((L))n_(cif). Herein, n_(cif) is a value of the CIF. Ifthe CIF is not configured for the wireless device, m′=m.

In a common search space, Y_(k) is set to 0 with respect to twoaggregation levels L=4 and L=8.

In a UE-specific search space of the aggregation level L, a variableY_(k) is defined by Equation 2 below.Y _(k)(A·Y _(k-1))mod D  [Equation 2]

Herein, Y⁻¹=n_(RNTI)≠0, A=39827, D=65537, k=floor(n_(s)/2), and n_(s)denotes a slot number in a radio frame.

When the UE monitors the PDCCH by using the C-RNTI, a search space and aDCI format used in monitoring are determined according to a transmissionmode of the PDSCH.

Meanwhile, when the UE monitors the PDCCH by using the C-RNTI, a searchspace and a DCI format used in monitoring are determined according to atransmission mode (TM) of the PDSCH. Table 3 below shows an example ofPDCCH monitoring for which the C-RNTI is configured.

TABLE 3 Transmission mode Transmission of PDSCH according mode DCIformat Search space to PDCCH Transmission DCI format 1A Public serviceand Single antenna mode 1 terminal specific port, port 0 DCI format 1Terminal specific Single antenna port, port 0 Transmission DCI format 1APublic service and Transmit diversity mode 2 terminal specific DCIformat 1 Terminal specific Transmit diversity Transmission DCI format 1APublic service and Transmit diversity mode 3 terminal specific DCIformat 2A Terminal specific CDD(Cyclic Delay Diversity) or transmitdiversity Transmission DCI format 1A Public service and Transmitdiversity mode 4 terminal specific DCI format 2 Terminal specificClosed-loop spatial multiplexing Transmission DCI format 1A Publicservice and Transmit diversity mode 5 terminal specific DCI format 1DTerminal specific MU-MIMO(Multi-user Multiple Input Multiple Output)Transmission DCI format 1A Public service and Transmit diversity mode 6terminal specific DCI format 1B Terminal specific Closed-loop spatialmultiplexing Transmission DCI format 1A Public service and If the numberof PBCH mode 7 terminal specific transmisison ports is 1, single antennaport, port 0. Otherwise, transmit diversity DCI format 1 Terminalspecific Single antenna port, port 5 Transmission DCI format 1A Publicservice and If the number of PBCH mode 8 terminal specific transmisisonports is 1, single antenna port, port 0. Otherwise, transmit diversityDCI format 2B Terminal specific Dual layer transmisison (port 7 or 8),or single antenna port, port 7 or 8 Transmission DCI format 1A Publicservice and Non-MBSFN sub- mode 9 terminal specific frame: if the numberof PBCH antenna ports is 1, port 0 is used as independent antenna port.Otherwise, transmit Diversity MBSFN sub-frame: port 7 as independentantenna port DCI format 2C Terminal specific 8 transmisison layers,ports 7-14 are used or port 7 or 8 is used as independent antenna portTransmission DCI 1A Public service and Non-MBSFN sub- mode 10 terminalspecific frame: if the number of PBCH antenna ports is 1, port 0 is usedas independent antenna port. Otherwise, transmit Diversity MBSFNsub-frame: port 7 as independent antenna port DCI format 2D Terminalspecific 8 transmisison layers, ports 7-14 are used or port 7 or 8 isused as independent antenna port

The usage of the DCI format is classified as shown in Table 3 below.

TABLE 4 DCI format Contents DCI format 0 Used in PUSCH scheduling DCIformat 1 Used in scheduling of one PDSCH codeword DCI format 1A Used incompact scheduling of one PDSCH codeword and random access process DCIformat 1B Used in compact scheduling of one PDSCH codeword havingprecoding information DCI format 1C Used in very compact scheduling ofone PDSCH codeword DCI format 1D Used in precoding and compactscheduling of one PDSCH codeword having power offset information DCIformat 2 Used in PDSCH scheduling of terminals configured in closed-loopspatial multiplexing mode DCI format 2A Used in PDSCH scheduling ofterminals configured in open-loop spatial multiplexing mode DCI format2B DCI format 2B is used for resouce allocation for dual-layerbeam-forming of PDSCH. DCI format 2C DCI format 2C is used for resouceallocation for closed-loop SU-MIMO or MU- MIMO operation to 8 layers.DCI format 2D DCI format 2C is used for resouce allocation to 8 layers.DCI format 3 Used to transmit TPC command of PUCCH and PUSCH having 2bit power adjustments DCI format 3A Used to transmit TPC command ofPUCCH and PUSCH having 1 bit power adjustment DCI format 4 Used in PUSCHscheduling of uplink (UP) operated in multi-antenna port transmisisonmode

FIG. 8 illustrates the architecture of a UL sub-frame in 3GPP LTE.

Referring to FIG. 8, the uplink sub-frame may be separated into acontrol region and a data region in the frequency domain. The controlregion is allocated a PUCCH (physical uplink control channel) fortransmission of uplink control information. The data region is allocateda PUSCH (physical uplink shared channel) for transmission of data (insome cases, control information may also be transmitted).

The PUCCH for one user equipment is allocated in resource block (RB)pair in the sub-frame. The resource blocks in the resource block pairtake up different sub-carriers in each of the first and second slots.The frequency occupied by the resource blocks in the resource block pairallocated to the PUCCH is varied with respect to a slot boundary. Thisis referred to as the RB pair allocated to the PUCCH having beenfrequency-hopped at the slot boundary. A frequency diversity gain may beobtained by transmitting uplink control information through differentsub-carriers over time.

Since the UE transmits UL control information over time throughdifferent subcarriers, a frequency diversity gain can be obtained. Inthe figure, m is a location index indicating a logical frequency-domainlocation of the RB pair allocated to the PUCCH in the sub-frame.

Uplink control information transmitted on the PUCCH may include a HARQACK/NACK, a channel quality indicator (CQI) indicating the state of adownlink channel, a scheduling request (SR) which is an uplink radioresource allocation request, and the like.

The PUSCH is mapped to a uplink shared channel (UL-SCH), a transportchannel. Uplink data transmitted on the PUSCH may be a transport block,a data block for the UL-SCH transmitted during the TTI. The transportblock may be user information. Or, the uplink data may be multiplexeddata. The multiplexed data may be data obtained by multiplexing thetransport block for the UL-SCH and control information. For example,control information multiplexed to data may include a CQI, a precodingmatrix indicator (PMI), an HARQ, a rank indicator (RI), or the like. Orthe uplink data may include only control information.

A carrier aggregation system is now described.

A carrier aggregation system aggregates a plurality of componentcarriers (CCs). A meaning of an existing cell is changed according tothe above carrier aggregation. According to the carrier aggregation, acell may signify a combination of a downlink component carrier and anuplink component carrier or an independent downlink component carrier.

Further, the cell in the carrier aggregation may be classified into aprimary cell, a secondary cell, and a serving cell. The primary cellsignifies a cell operated in a primary frequency. The primary cellsignifies a cell which UE performs an initial connection establishmentprocedure or a connection reestablishment procedure or a cell indicatedas a primary cell in a handover procedure. The secondary cell signifiesa cell operating in a secondary frequency. Once the RRC connection isestablished, the secondary cell is used to provided an additional radioresource.

As described above, the carrier aggregation system may support aplurality of component carriers (CCs), that is, a plurality of servingcells unlike a single carrier system.

The carrier aggregation system may support a cross-carrier scheduling.The cross-carrier scheduling is a scheduling method capable ofperforming resource allocation of a PDSCH transmitted through othercomponent carrier through a PDCCH transmitted through a specificcomponent carrier and/or resource allocation of a PUSCH transmittedthrough other component carrier different from a component carrierbasically linked with the specific component carrier.

Meanwhile, the PDCCH is monitored in an area restricted to the controlregion in the subframe, and a CRS transmitted in a full band is used todemodulate the PDCCH. As a type of control data is diversified and anamount of control data is increased, scheduling flexibility is decreasedwhen using only the existing PDCCH. In addition, in order to decrease anoverhead caused by CRS transmission, an enhanced PDCCH (EPDCCH) isintroduced.

FIG. 9 illustrates a subframe having an EPDCCH.

A subframe may include a zero or one PDCCH region 410 or zero or moreEPDCCH regions 420 and 430.

The EPDCCH regions 420 and 430 are regions in which a wireless devicemonitors an EPDCCH. The PDCCH region 410 is located in up to four frontOFDM symbols of a subframe, while the EPDCCH regions 420 and 430 mayflexibly be scheduled in OFDM symbols after the PDCCH region 410.

One or more EPDCCH regions 420 and 430 may be designated for thewireless device, and the wireless devices may monitor an EPDCCH in thedesignated EPDCCH regions 420 and 430.

The number/location/size of the EPDCCH regions 420 and 430 and/orinformation on a subframe for monitoring an EPDCCH may be provided by abase station to a wireless device through an RRC message or the like.

In the PDCCH region 410, a PDCCH may be demodulated based on a CRS. Inthe EPDCCH regions 420 and 430, a demodulation (DM) RS may be defined,instead of a CRS, for demodulation of an EPDCCH. An associated DM RS maybe transmitted in the corresponding EPDCCH regions 420 and 430.

An RS sequence r_(ns)(m) for the associated DM RS is represented byEquation 3.

$\begin{matrix}{{r_{l,{ns}}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Here, m=0, 1, . . . , 2N_(maxRB)−1, N_(maxRB) denotes the maximum numberof RBs, ns denotes the number of a slot in a radio frame, and l denotesthe number of an OFDM symbol in a slot.

A pseudo-random sequence c(i) is defined by the following gold sequencewith a length of 31.

Here, m=0, 1, . . . , 12N_(RB)−1, and N_(RB) denotes the maximum numberof RBs. A pseudo-random sequence generator may be initialized asc_(init)=(floor(ns/2)+1)(2N_(EPDCCH,ID)+1)2¹⁶+n_(EPDCCH,SCID) in eachstarting subframe. ns is the number of a slot in a radio frame,N_(EPDCCH,ID) is a value associated with an EPDCCH set, which is giventhrough a higher-layer signal, and n_(EPDCCH,SCID) is a specific value.

The EPDCCH regions 420 and 430 may be used for scheduling for differentcells, respectively. For example, an EPDCCH in the EPDCCH region 420 maycarry scheduling information for a primary cell, and an EPDCCH in theEPDCCH region 430 may carry scheduling information for a secondary cell.

When EPDCCHs are transmitted in the EPDCCH regions 420 and 430 throughmultiple antennas, the same precoding as for the EPDCCHs may be appliedto DM RSs in the EPDCCH regions 420 and 430.

Comparing with a CCE used as a transmission resource unit for a PDCCH, atransmission resource unit for an EPDCCH is an enhanced control channelelement (ECCE). An aggregation level may be defined as a resource unitfor monitoring an EPDCCH. For example, defining one ECCE as a minimumresource for an EPDCCH, an aggregation level may be defined as L={1, 2,4, 8, 16}.

Hereinafter, an EPDCCH search space may correspond to an EPDCCH region.In an EPDCCH search space, one or more EPDCCH candidates may bemonitored by one or more aggregation levels.

Hereinafter, resource allocation for an EPDCCH will be described.

An EPDCCH is transmitted using one or more ECCEs. An ECCE includes aplurality of enhanced resource element groups (EREGs). An ECCE mayinclude four EREGs or eight EREGs according to a subframe type based ona TDD DL-UL configuration and a CP. For example, an ECCE may includefour EREGs in a normal CP, while an ECCE may include eight EREGs in anextended CP.

A physical resource block (PRB) pair refers to two PRBs having the sameRB number in one subframe. A PRB pair refers to a first PRB of a firstslot and a second PRB of a second slot in the same frequency domain. Ina normal CP, a PRB pair includes 12 subcarriers and 14 OFDM symbols andthus includes 168 REs.

FIG. 10 illustrates an example of a PRB pair.

Although it is shown below that a subframe includes two slots and a PRBpair in one slot includes seven OFDM symbols and 12 subcarriers, thesenumbers of OFDM symbols and subcarriers are provided for illustrativepurposes only.

In one subframe, a PRB pair includes 168 REs. 16 EREGs are formed from144 Res, excluding 24 REs for a DM RS. Thus, one EREG may include nineREs. Here, a CSI-RS or CRS may be disposed in one PRB pair in additionthe DM RM. In this case, the number of available REs may be reduced andthe number of REs included in one EREG may be reduced. The number of REsincluded in an EREG may change, while the number of EREGs included inone PRB pair, 16, does not change.

Here, as illustrated in FIG. 10, REs may sequentially be assignedindexes, starting from a top subcarrier in a leftmost OFDM symbol (l=0)(or REs may sequentially be assigned indexes in an upward direction,starting from a bottom subcarrier in the leftmost OFDM symbol (l=0)).Suppose that 16 EREGs are assigned indexes from 0 to 15. Here, nine REshaving RE index 0 are allocated to EREG 0. Likewise, nine REs having REindex k (k=0, . . . , 15) are allocated to EREG k.

A plurality of EREGs is combined to define an EREG group. For example,an EREG group including four EREGs may be defined as follows: EREG group#0={EREG 0, EREG 4, EREG 8, EREG 12}, EREG group #1={EREG 1, EREG 5,EREG 9, EREG 3}, EREG group #2={EREG 2, EREG 6, EREG 10, EREG 14}, andEREG group #3={EREG 3, EREG 7, EREG 11, EREG 15}. An EREG groupincluding eight EREGs may be defined as follows: EREG group #0={EREG 0,EREG 2, EREG 4, EREG 6, EREG 8, EREG 10, EREG 12, EREG 14} and EREGgroup #1={EREG 1, EREG 3, EREG 5, EREG 7, EREG 9, EREG 11, EREG 13, EREG15}.

As described above, an ECCE may include four EREGs, and an ECCE mayinclude eight EREGs in an extended CP. An ECCE is defined by an ERGEgroup. For example, FIG. 6 shows that ECCE #0 includes EREG group #0,ECCE #1 includes EREG group #1, ECCE #2 includes EREG group #2, and ECCE#3 includes EREG group #3.

There are localized transmission and distributed transmission inECCE-to-EREG mapping. In localized transmission, an EREG group formingone ECCE is selected from EREGs in one PRB pair. In distributedtransmission, an EREG group forming one ECCE is selected from EREGs indifferent PRB pairs.

Hereinafter, machine-type communication (MTC) will be described.

FIG. 11a illustrates an example of MTC.

MTC refers to an information exchange between MTC devices 100 via a BS200 or information exchange between an MTC device 100 and an MTC server700 via a BS without involving human interactions.

The MTC server 700 is an entity to communicate with the MTC device 100.The MTC server 700 runs an MTC application and provides the MTC devicewith an MTC-specific service.

The MTC device 100 is a wireless device to provide MTC communication,which may be stationary or mobile.

Services provided through MTC are differentiated from existingcommunication services involving human intervention and an MTC servicerange is wide, for example, tracking, metering, payment, medicalservices, remote control, or the like. More specifically, examples ofMTC services may include reading a meter, measuring a water level,utilizing a surveillance camera, inventory reporting of a vendingmachine, etc.

The MTC device is characterized in that a transmission data amount issmall and uplink/downlink data transmission/reception occurs sometimes.Therefore, it is effective to decrease a unit cost of the MTC device andto decrease battery consumption according to a low data transmissionrate. The MTC device is characterized by low mobility and thus has achannel environment that hardly changes.

FIG. 11b illustrates an example of cell coverage extension for an MTCdevice.

Recently, extension of cell coverage of a BS is considered for an MTCdevice 100, and various schemes for extending cell coverage are underdiscussion.

However, when the cell coverage is extended, if the BS transmits a PDSCHand a (E)PDCCH including scheduling information on the PDSCH to an MTCdevice located in the coverage extension region as if transmitting thePDSCH and the (E)PDCCH to a normal UE, the MTC device has difficulty inreceiving the PDSCH and the (E)PDCCH.

Here, (E)PDCCH refers to a PDCCH or EPDCCH (E-PDCCH).

<Disclosures of the Present Specification>

Thus, disclosures of the present specification are provided to solve theforegoing problem.

A method according to a disclosure of the present specification is amethod for an MTC device to receive a downlink control channel, themethod including: receiving configuration information on a maximumnumber of physical resource blocks (PRBs) which are available for a basestation to transmit the downlink control channel; receivingconfiguration information on a set of PRBs for monitoring controlchannel in which the MTC device needs to monitor the downlink controlchannel; and monitoring the downlink control channel on the PRBsaccording to the configuration information on the set of PRBs formonitoring control channel.

In this case, when a number of the PRBs based on the set of PRBs formonitoring control channel exceeds the maximum number of PRBs, thedownlink control channel may be monitored only on a set of a number ofPRBs equal to or less than the maximum number of PRBs.

Here, the maximum number of PRBs for the downlink control channel may be6.

Further, the downlink control channel may be monitored only on a set ofa number of PRBs having a relatively low PRB index, equal to or lessthan the maximum number of PRBs, in the set of PRBs for monitoringcontrol channel.

Further, the MTC device may assume that PRBs in which the downlinkcontrol channel is not monitored in the set of PRBs for monitoringcontrol channel are punctured or rate-matched.

Further, the set of PRBs for monitoring control channel may be setindependently of a set of data channel monitoring PRBs in which the MTCdevice needs to monitor a downlink data channel.

Further, the set of PRBs for monitoring control channel may be set thesame as a set of data channel monitoring PRBs in which the MTC deviceneeds to monitor a downlink data channel.

Further, the maximum number of PRBs for the downlink control channel maybe set independently of a maximum number of PRBs which are available forthe base station to transmit a downlink data channel.

Further, the maximum number of PRBs for the downlink control channel maybe set such that a sum of the maximum number of PRBs for the downlinkcontrol channel and a maximum number of PRBs which are available for thebase station to transmit a downlink data channel is a reference PRBnumber. Here, the reference PRB number may be 6.

For example, the downlink control channel may be an EPDCCH, and thedownlink data channel may be a PDSCH.

The disclosures of the present specifications are described in detail asfollows.

As described above, an MTC device (or MTC UE) has a small amount of datato transmit and occasionally performs uplink/downlink datatransmission/reception. Therefore, it is efficient to decrease a unitcost of a terminal and to decrease battery consumption according to alow data transmission rate.

The MTC device is characterized by low mobility and thus has a channelenvironment that hardly changes. In LTE-A, it is currently considered toincrease existing coverage for the MTC UE. To this end, various coverageenhancement schemes for the MTC UE are under discussion as follows.

The maximum bandwidth supported by normal LTE UEs is 20 MHz. Onepotential technique to reduce the UE cost is to reduce the maximumbandwidth that the UE supports from 20 MHz to a lower bandwidth (e.g.,1.4 MHz, 3 MHz or 5 MHz). The reduction of the maximum bandwidth can beapplied to the downlink and/or uplink, the RF and/or basebandcomponents, the data and/or control channels. To be more specific, thefollowing options have been considered and evaluated, which allow thebandwidth reduction on the DL and UL to be considered separately.

DL

Option DL-1: Reduced bandwidth for both RF and baseband

Option DL-2: Reduced bandwidth for baseband only for both data channeland control channels

Option DL-3: Reduced bandwidth for data channel in baseband only, whilethe control channels are still allowed to use the carrier bandwidth

UL

Option UL-1: Reduced bandwidth for both RF and baseband

Option UL-2: No bandwidth reduction

This option does not have any impact on coverage, power consumption,specifications, performance, and UE cost.

For all these options, the reduced bandwidth is assumed to be no lessthan 1.4 MHz, and the frequency location of the reduced bandwidth isassumed to be fixed at the center of the carrier bandwidth. Technically,any combination of the DL and UL options is possible. However, some ofthe combinations may make more practical sense. For example, DL-2 wouldbe a more natural choice than DL-1 when combined with UL-2.

Note that this is not intended to be an exhaustive list of the possibleoptions. Some interesting variations of these options could allow thefrequency location of the reduced bandwidth to be changedsemi-statically, dynamically, or in a pre-defined pattern for each UE.Some of these variations could potentially allow more MTC UEs to besupported in the system. Taking the extension of DL-3 as an example,

If the frequency location of the data channel is semi-staticallyconfigured, it is expected to provide the same cost saving as DL-3, withsome additional specification impact.

If the frequency location of the data channel is dynamically changedusing grants, it would be the same as one of the techniques for reducedpeak rate, restricting the number of PRBs, as discussed in Section 6.4.

Nonetheless, the discussion in this section is restricted to the optionslisted above.

With reduced bandwidth, the cost of RF and baseband components canpotentially be reduced. Depending on which option is assumed, therelative cost savings and the specification impact can be different.

Particularly, the disclosures of the present specification may relate toOption DL-3 among the foregoing downlink bandwidth reduction options.

However, it would be obvious to those skilled in the art that thedisclosures of the present specification are also applicable to theother options illustrated above.

Further, it would be obvious that the disclosures of the presentspecification are applicable to general UEs of small bandwidths as wellas the MTC device or MTC UE.

Specifically, in a next-generation LTE-A system, a downlink channelbandwidth of 1.4 MHz or 6 RBs (or PRBs) may be suggested for low-cost orlow-complexity MTC devices.

For example, although a PDCCH is transmitted via the entire downlinksystem bandwidth (for example, 10 MHz or 50 RBs), the maximum PDSCHbandwidth for a PDSCH may be 1.4 MHz or 6 RBs (or PRBs).

Alternatively, both a PDCCH and a PDSCH may be transmitted, for example,via 1.4 MHz or 6 RBs (or PRBs).

FIG. 12 illustrates an example of a PDSCH monitoring PRB region for anMTC device.

Referring to FIG. 12, defining a PRB region for transmitting a PDSCH asPDSCH_monitoring_PRB and the maximum bandwidth (or the number of PRBs)for transmitting a PDSCH as Max_PDSCH_BW for convenience, Max_PDSCH_BWmay be 1.4 MHz (6 RBs).

Here, PDSCH_monitoring_PRB may denote a set of data channel monitoringPRBs in which the MTC device needs to monitor a downlink data channel,and Max_PDSCH_BW may denote the maximum number of PRBs available for abase station to transmit the downlink data channel.

In the disclosures of the present specification, it is assumed thatMax_PDSCH_BW is 1.4 MHz or 6 PRBs. Here, PDSCH_monitoring_PRB mayinclude six non-contiguous PRBs.

In this case, Max_PDSCH_BW may denote the number of non-contiguous PRBs(or the total length of regions (in Hz)) for transmitting a PDSCH.

It would be obvious to those skilled in the art that the disclosures ofthe present specification are applicable the same to differentMax_PDSCH_BW in addition to 1.4 Hz (6 RBs).

Meanwhile, an EPDCCH may be used for low-cost MTC using a reduced PDSCHbandwidth. In this case, it may be also considered to reduce a bandwidthfor transmitting the EPDCCH for the low cost of an MTC device.

Therefore, the disclosures of the present specification suggest settingmodes of a reduced bandwidth for an EPDCCH as follows.

<Bandwidth Restriction for EPDCCH>

An EPDCCH may be used for a low-cost MTC device using a reduced PDSCHbandwidth. In this case, it may be also considered to reduce a bandwidthfor transmitting the EPDCCH for the low cost of the MTC device.

Here, EPDCCH_monitoring_PRB may denote a set of PRBs for monitoring thecontrol channel in which the MTC device needs to monitor a downlinkcontrol channel, and Max_EPDCCH_BW may denote the maximum number of PRBsavailable for a base station to transmit the downlink data channel.

In this case, EPDCCH_monitoring_PRB may include non-contiguous PRBs. Inthis case, Max_EPDCCH_BW may denote the number of non-contiguous PRBs(or the total length of regions (in Hz)) for transmitting an EPDCCH.

The following modes may be used to set up EPDCCH_monitoring_PRBaccording to the disclosures of the present specification.

Setting Mode A

According to setting mode A, EPDCCH_monitoring_PRB may be setindependently of PDSCH_monitoring_PRB.

That is, according to setting mode A, a set of PRBs for monitoringcontrol channel may be set independently of a set of data channelmonitoring PRBs in which the MTC device needs to monitor a downlink datachannel.

Setting Mode B

According to setting mode B, EPDCCH_monitoring_PRB may be set the sameas PDSCH_monitoring_PRB.

That is, a set of PRBs for monitoring control channel may be set thesame as a set of data channel monitoring PRBs in which the MTC deviceneeds to monitor a downlink data channel.

Further, when Max_EPDCCH_BW is greater than Max_PDSCH_BW,EPDCCH_monitoring_PRB may be set to always include PDSCH_monitoring_PRB.

Further, when Max_EPDCCH_BW is smaller than Max_PDSCH_BW,EPDCCH_monitoring_PRB may be set to be always included inPDSCH_monitoring_PRB.

In addition, the following modes may be used to set up Max_EPDCCH_BW asthe maximum bandwidth for transmitting an EPDCCH according to thedisclosures of the present specification.

Setting Mode 1

According to setting mode 1, Max_EPDCCH_BW may be set independently ofMax_PDSCH_BW.

That is, the maximum number of PRBs for a downlink control channel maybe set independently of the maximum number of PRBs available for a basestation to transmit a downlink data channel.

For example, when Max_PDSCH_BW is 6 RBs, Max_EPDCCH_BW may be set to 4RBs.

Setting Mode 2

According to setting mode 2, defining a bandwidth of a PRB regionincluding EPDCCH_monitoring_PRB and PDSCH_monitoring_PRB asMax_PDSCH_EPDCCH_BW, Max_PDSCH_EPDCCH_BW may be set to be specific PRBsor reference PRBs (for example, 6 PRBs).

That is, the maximum number of PRBs for a downlink control channel maybe set such that the sum of the maximum number of PRBs for the downlinkcontrol channel and the maximum number of PRBs available for the basestation to transmit a downlink data channel is specific PRBs orreference PRBs. Here, the number of reference PRBs may be 6.

For example, when EPDCCH_monitoring_PRB includes PRBs of indexes 1 to 4and PDSCH_monitoring_PRB includes PRBs of indexes 2 to 6,Max_PDSCH_EPDCCH_BW, that is, the number of PRBs in a PRB regionincluding EPDCCH_monitoring_PRB and PDSCH_monitoring_PRB, is 6 PRBs,which satisfies the given condition.

Further, for example, when EPDCCH_monitoring_PRB includes PRBs ofindexes of and 4 and PDSCH_monitoring_PRB includes PRBs of indexes 6 to9, Max_PDSCH_EPDCCH_BW, that is, the number of PRBs in a PRB regionincluding EPDCCH_monitoring_PRB and PDSCH_monitoring_PRB, is 6 PRBs,which satisfies the given condition.

Therefore, according to setting mode 2, the number of PRBs available forEPDCCH_monitoring_PRB and PDSCH_monitoring_PRB may vary depending on thepositions/configurations of EPDCCH_monitoring_PRB andPDSCH_monitoring_PRB.

Hereinafter, the aforementioned setting mode 1 of the Max_EPDCCH_BWsetting modes will be described in detail as a first aspect of thedisclosures of the present specification and the aforementioned settingmode 2 of the Max_EPDCCH_BW setting modes will be described in detail asa second aspect of the disclosures of the present specification.

<First Aspect of Disclosures of the Present Specification: IndependentSetting of Max_EPDCCH_BW>

The first aspect of the disclosures of the present specification isdescribed assuming that the maximum bandwidth for transmitting an EPDCCHis set up according to the aforementioned setting mode 1. However, itwould be obvious to those skilled in the art that the aforementionedsetting mode 2 is applicable to the technique disclosed in the firstaspect of the disclosures of the present specification.

To set up Max_EPDCCH_BW independently of Max_PDSCH_BW for a low-cost MTCdevice with a limited buffer size as in setting mode 1, it may notallowed to receive a PDCCH in an EPDCCH transmitting subframe.

Thus, the first aspect of the disclosures of the present specificationsuggests that the MTC device not monitor a CSS (and a USS) transmittedvia a PDCCH assuming that a CSS (and a USS) is not transmitted via aPDCCH in an EPDCCH monitoring subframe.

For example, although Max_EPDCCH_BW is set to 6 PRBs, the MTC device orUE may be assigned, by the base station (eNodeB), a PRB set for anEPDCCH including 8 PRBs for monitoring an EPDCCH, that is, an EPDCCH PRBset.

As such, when the MTC device is assigned, by the eNodeB, an EPDCCH PRBset including a PRB region that is greater than Max_EPDCCH_BW, the MTCdevice may receive an EPDCCH via the EPDCCH PRB set according to thefollowing method.

The MTC device may receive the EPDCCH only via Max_EPDCCH_BW (forexample, six) PRBs having lower (or higher) PRB indexes. Here, the MTCdevice may assume that the EPDCCH is transmitted via puncturing orrate-matching in a PRB region that the MTC device is unable to receivein the PRB region forming the EPDCCH PRB set.

That is, the MTC device may monitor the downlink control channel only ona set of a number of PRBs having relatively lower PRB indexes, equal toor smaller than the maximum number of PRBs, in the set of PRBs formonitoring control channel, assuming that PRBs in which the downlinkcontrol channel is not monitored in the set of the PRBs for monitoringcontrol channel are punctured or rate-matched.

When the MTC device having limited Max_EPDCCH_BW is assigned multipleEPDCCH PRB sets by the base station and the number of PRBs in a regionincluding two EPDCCH PRB sets exceeds Max_PDSCH_EPDCCH_BW (for example,6 PRBs), PRB regions received by the MTC device may be prioritized asfollows.

1) A PRB region of an EPDCCH PRB set having a low index

2) A PRB region having a low index in the same EPDCCH PRB set

That is, for example, in a case where Max_EPDCCH_BW is 6 PRBs, when theMTC device is assigned two EPDCCH PRB sets including 4 PRBs, the MTCdevice may receive the entire PRB region of EPDCCH PRB set 0 and mayreceive 2 PRBs having lower indexes in EPDCCH PRB set 1. Here, the MTCdevice may assume that the EPDCCH is transmitted via puncturing orrate-matching in a PRB region that the MTC device is unable to receivein the PRB region forming the EPDCCH PRB set.

<Second Aspect of Disclosures of the Present Specification: Restrictionof Max_EPDCCH_BW>

The second aspect of the disclosures of the present specification isdescribed assuming that the maximum bandwidth for transmitting an EPDCCHis set up according to the aforementioned setting mode 2.

However, it would be obvious that the idea of the present invention isalso applicable even when setting mode 2 is not employed.

Hereinafter, the second aspect of the disclosures of the presentspecification is described with reference to separate cases, which are afirst embodiment where cross subframe scheduling is used and a secondembodiment where same-subframe scheduling with semi-staticPDSCH_monitoring_PRB allocation is used.

First Embodiment of Second Aspect: Cross Subframe Scheduling

According to the first embodiment of the second aspect, when schedulingwith a PDCCH and/or EPDCCH is performed for PDSCH transmission to thelow-cost MTC device, cross subframe scheduling may be employed.

FIG. 13 illustrates an example of cross subframe scheduling for an MTCdevice.

Referring to FIG. 13, when a PDSCH is scheduled through a PDCCH orEPDCCH in subframe n−1 (or subframe preceding subframe n−1), thescheduled PDSCH may be transmitted through the PDCCH or EPDCCH insubframe n.

In this case, as illustrated in FIG. 13, the scheduled PDSCH may betransmitted in subframe n through cross subframe scheduling. Further,the EPDCCH may also be transmitted in subframe n. Here, a PDSCHmonitoring PRB in subframe n may be a PRB region in which the scheduledPDSCH is transmitted. Further, an EPDCCH monitoring PRB may be a PRBregion for transmitting the EPDCCH (for example, a PRB region formingEPDCCH PRB sets).

Here, a bandwidth of a PRB region including the PDSCH monitoring PRB andthe EPDCCH monitoring PRB in subframe n may exceed Max_PDSCH_EPDCCH_BW(for example, 6 RBs). To prevent this situation or in the occurrence ofthis situation, the second embodiment of the second aspect of thedisclosures of the present specification suggests that the PDSCH andEPDCCH be received as follows.

Reception Mode 1-1

According to reception mode 1-1, when the number of PRBs in a regionincluding PDSCH monitoring PRBs (PDSCH transmitting PRB region) andEPDCCH monitoring PRBs in a specific subframe exceedsMax_PDSCH_EPDCCH_BW (for example, 6 RBs), the MTC device does notperform EPDCCH monitoring (EPDCCH reception) in that subframe.

That is, the MTC device assumes that no EPDCCH is transmitted in thatsubframe.

Reception Mode 1-2

According to reception mode 1-2, the MTC device does not perform EPDCCHmonitoring in a PDSCH-scheduled subframe.

That is, the MTC device may assume that no EPDCCH is transmitted in thePDSCH-scheduled subframe.

Reception Mode 1-3

According to reception mode 1-3, the MTC device monitors a PDCCH in aPDSCH-scheduled subframe.

That is, although subframe n is an EPDCCH monitoring subframe, if aPDSCH is transmitted in that subframe, the MTC device may assume thatDCI is transmitted through a PDCCH, not through an EPDCCH.

Reception Mode 1-4

According to reception mode 1-4, when the number of PRBs in a regionincluding PDSCH monitoring PRBs (PDSCH transmitting PRB region) andEPDCCH monitoring PRBs in a specific subframe exceedsMax_PDSCH_EPDCCH_BW (for example, 6 RBs), PRB regions received by theMTC device may be prioritized as follows.

1) A PDSCH transmitting PRB region

2) A PRB region forming an EPDCCH PRB set having a low index in a caseof a plurality of EPDCCH PRB sets

3) A PRB having a low PRB index in a PRB region forming an EPDCCH PRBset

Here, there may be an EPDCCH PRB region which is not received accordingto the foregoing priorities. Here, the MTC device may assume that theEPDCCH is transmitted via puncturing or rate-matching in the PRB regionwhich is not received according to the foregoing priorities in the PRBregion forming the EPDCCH PRB set.

Second Embodiment of Second Aspect: Same-Subframe Scheduling withSemi-Static PDSCH_Monitoring_PRB Allocation

According to the second embodiment of the second aspect, when schedulingwith a PDCCH and/or EPDCCH is performed for PDSCH transmission to thelow-cost MTC device, a semi-static PRB region for transmitting a PDSCH(for example, PDSCH_monitoring_PRB) may be determined and a PDSCHtransmitting PRB region may be designated with a PDCCH and/or EPDCCHwithin the PRB region (PDSCH location(s) within a limited number ofsemi-static PRBs, with (E)PDCCH within same subframe to indicate exactresource allocation).

Here, a bandwidth of a PRB region including PDSCH monitoring PRBs andEPDCCH monitoring PRBs may exceed Max_PDSCH_EPDCCH_BW (for example, 6RBs). To prevent this situation or in the occurrence of this situation,the first embodiment of the second aspect of the disclosures of thepresent specification suggests that the PDSCH and EPDCCH be received asfollows.

Reception Mode 2-1

According to reception mode 2-1, when the number of PRBs in a regionincluding PDSCH monitoring PRBs and EPDCCH monitoring PRBs in a specificsubframe exceeds Max_PDSCH_EPDCCH_BW (for example, 6 RBs), the MTCdevice does not perform EPDCCH monitoring (EPDCCH reception) in thatsubframe.

That is, the MTC device assumes that no EPDCCH is transmitted in thatsubframe.

Reception Mode 2-2

According to reception mode 2-2, the foregoing setting mode B isemployed to prevent the bandwidth of the PRB region including the PDSCHmonitoring PRB and the EPDCCH monitoring PRB from exceedingMax_PDSCH_EPDCCH_BW (for example, 6 RB s).

That is, EPDCCH_monitoring_PRB may be set to be always the same asPDSCH_monitoring_PRB. Alternatively, when Max_EPDCCH_BW is greater thanMax_PDSCH_BW, EPDCCH_monitoring_PRB may be set to always includePDSCH_monitoring_PRB. When Max_EPDCCH_BW is smaller than Max_PDSCH_BW,EPDCCH_monitoring_PRB may be set to be always included inPDSCH_monitoring_PRB.

Reception Mode 2-3

According to reception mode 2-3, when the number of PRBs in a regionincluding PDSCH monitoring PRBs and EPDCCH monitoring PRBs in a specificsubframe exceeds Max_PDSCH_EPDCCH_BW (for example, 6 RBs), PRB regionsreceived by the MTC device may be prioritized as follows.

1) A PDSCH monitoring PRB region

2) A PRB region forming an EPDCCH PRB set having a low index in a caseof a plurality of EPDCCH PRB sets

3) A PRB having a low PRB index in a PRB region forming an EPDCCH PRBset

There may be an EPDCCH PRB region which is not received according to theforegoing priorities. Here, the MTC device may assume that the EPDCCH istransmitted via puncturing or rate-matching in the PRB region which isnot received in the PRB region forming the EPDCCH PRB set.

Here, the MTC device may assume that EPDCCH_monitoring_PRB (EPDCCH PRBset(s)) is PDSCH_monitoring_PRB, without being assigned separatePDSCH_monitoring_PRB from the base station.

Hereinafter, additional disclosures of the present specification areillustrated.

<Additional Disclosure of the Present Specification—Collision BetweenEPDCCH and PDSCH Transmission Resources>

Meanwhile, a PDSCH may be scheduled for a low-cost MTC device throughcross subframe scheduling.

Thus, as illustrated in FIG. 13, a PDSCH scheduled with a PDCCH orEPDCCH prior to subframe n−1 may be transmitted to the MTC device insubframe n, and the MTC device may receive an EPDCCH in subframe n.

Here, when the MTC device receives an EPDCCH in subframe n and PDSCHtransmitting REs (or PRBs) scheduled via the EPDCCH and via a PDCCH orEPDCCH prior to subframe n−1 (or scheduled semi-persistently) overlap orto prevent the PDSCH transmitting REs (or PRBs) from overlapping, theadditional disclosure of the present specification suggest that the MTCdevice operate as follows.

Mode 3-1

According to mode 3-1, when a PDSCH transmitting PRB region andEPDCCH_monitoring_PRB (PRB region forming an EPDCCH PRB set(s)) overlapin a PDSCH-scheduled subframe, it is assumed that the PDSCH istransmitted through a PDSCH transmitting region scheduled for the MTCdevice.

RE (or PRB) resources for transmitting EPDCCH, which are overlapped withthose for a PDSCH are punctured or rate-matched.

Mode 3-2

According to mode 3-2, when a PDSCH transmitting PRB region andEPDCCH_monitoring_PRB (PRB region forming an EPDCCH PRB set(s)) overlapin a PDSCH-scheduled subframe, it is assumed that the PDSCH istransmitted through a PDSCH transmitting region scheduled for the MTCdevice.

The MTC device may assume that no EPDCCH is transmitted in an EPDCCHcandidate overlapping with a PDSCH RE (or PRB) resource.

Mode 3-3

According to mode 3-3, when a PDSCH transmitting PRB region andEPDCCH_monitoring_PRB (PRB region forming an EPDCCH PRB set(s)) overlapin a PDSCH-scheduled subframe, it is assumed that a PDSCH is transmittedvia puncturing or rate-matching in an RE (or PRB) region overlappingwith a transmission region for an EPDCCH received (successfully decoded)by the MTC device.

Mode 3-4

According to mode 3-4, when a PDSCH transmitting PRB region andEPDCCH_monitoring_PRB (PRB region forming an EPDCCH PRB set(s)) overlapin a PDSCH-scheduled subframe, the MTC device assumes that a PDSCH stransmitted via puncturing or rate-matching in a PRB region overlappingwith EPDCCH_monitoring_PRB.

Mode 3-5

According to mode 3-5, the MTC device does not perform EPDCCH monitoringin a PDSCH-scheduled subframe.

That is, the MTC device may assume that no EPDCCH is transmitted in thePDSCH-scheduled subframe.

Mode 3-6

According to mode 3-6, when a PDSCH transmitting PRB region andEPDCCH_monitoring_PRB (PRB region forming an EPDCCH PRB set(s)) overlapin a PDSCH-scheduled subframe, the MTC device does not perform EPDCCHmonitoring.

Mode 3-7

According to mode 3-7, the MTC device assumes that a PDSCH istransmitted through a PDSCH transmitting region scheduled for the MTCdevice.

When a PDSCH transmitting PRB region overlaps with a PRB region of aspecific EPDCCH PRB set, it is assumed that no EPDCCH is transmitted inthe EPDCCH PRB set (no EPDCCH monitoring is performed in the EPDCCH PRBset).

<Another Additional Disclosure of the Present Specification—EPDCCHCandidates>

Meanwhile, according to 3GPP TS 36.213, the number of EPDCCH candidatesto be monitored by the MTC device may be determined based on anaggregation level, the number of PRBs (that is, the number of PRB pairs)in an EPDCCH PRB set, an EPDCCH transmission mode (a localized EPDCCHtransmission mode or a distributed EPDCCH transmission mode), and anyone of case 1, case 2 and case 3. Here, case 1, case 2, and case 3 aredetermined based on a used DCI format or on whether a used CP is anormal CP or extended CP.

Case 1 to case 3 may apply as follows.

Case 1 applies as below.

1. For normal subframes and a normal downlink cyclic prefix (CP) whenDCI formats 2/2A/2B/2C/2D are monitored and {circumflex over (N)}_(RB)^(DL)≥25.

2. For special subframes with special subframe configurations 3, 4, and8 and a normal downlink CP when DCI formats 2/2A/2B/2C/2D are monitored.

3. For normal subframes and a normal downlink CP when DCI formats1A/1B/1D/1/2/2A/2B/2C/2D/0/4 are monitored and n_(EPDCCH)<104.

4. For special subframes with special subframe configurations 3, 4, and8, a normal downlink CP when DCI formats 1A/1B/1D/1/2A/2/2B/2C/2D/0/4are monitored, and n_(EPDCCH)<104.

Here, n_(EPDCCH) denotes the number of downlink REs in a PRB pairconfigured for possible EPDCCH transmission of an EPDCCH set.

Case 2 applies as below.

1. For normal subframes and an extended downlink CP when DCI formats1A/1B/1D/1/2A/2/2B/2C/2D/0/4 are monitored.

2. For special subframes with special subframe configurations 1, 2, 6,7, and 9 and a normal downlink CP when DCI formats1A/1B/1D/1/2A/2/2B/2C/2D/0/4 are monitored.

3. For special subframes with special subframe configurations 1, 2, 3,5, and 6 and an extended downlink CP when DCI formats1A/1B/1D/1/2A/2/2B/2C/2D/0/4 are monitored.

Case 3 applies in other cases.

According to the above details and 3GPP TS 36.213, an aggregation levelfor constructing an EPDCCH PRB set and the number of EPDCCH candidatesby the aggregation level (AL) may change depending on case 1, case 2,and case 3, and a case which each cell belongs to is associated withN_(RB) ^(DL) ({circumflex over (N)}_(RB) ^(DL)=N_(RB) ^(DL) of theserving cell on which EPDCCH is monitored).

This is because the size of a resource allocation (RA) field of DCIchanges depending on N_(RB) ^(DL) (downlink system bandwidth) andaccordingly the number of ECCEs forming the DCI needs to change.

Meanwhile, it is considered for the low-cost MTC device to use adownlink channel bandwidth of 1.4 MHz for a data channel.

Thus, although a PDCCH is transmitted via the entire downlink systembandwidth (for example, 10 MHz or 50 RBs), a PDSCH may be transmittedvia the maximum PDSCH bandwidth (for example, 6 RBs).

In this case, the size of DCI transmitted to the low-cost MTC device maychange depending on a restricted PDSCH bandwidth (Max_PDSCH_BW), not onthe downlink system bandwidth.

Therefore, according to the other additional disclosure of the presentspecification, when DCI is transmitted to the low-cost MTC device via anEPDCCH, {circumflex over (N)}_(RB) ^(DL) denotes Max_PDSCH_BW (that is,the size of the maximum PRB region for transmitting data (PDSCH)).

Alternatively, according to the other additional disclosure of thepresent specification, case 3 (or case 2) having a large number ofEPDCCH candidates with a small aggregation level is always applied forthe low-cost MTC device that may have a restricted size of PRBs fortransmitting an EPDCCH.

The aforementioned details may be applied not only to an MTC device thatneeds coverage extension but also to an MTC device not needing coverageextension (for example, an MTC device that performs 0 dB coverageenhancement), a low-cost MTC device, or a low-complexity MTC device.

The aforementioned embodiments of the present invention can beimplemented through various means. For example, the embodiments of thepresent invention can be implemented in hardware, firmware, software,combinations thereof, etc. Details thereof will be described withreference to the drawing.

FIG. 14 is a block diagram of a wireless communication system accordingto a disclosure of the present specification.

A BS 200 includes a processor 201, a memory 202, and a radio frequency(RF) unit 203. The memory 202 is coupled to the processor 201, andstores various pieces of information for driving the processor 201. TheRF unit 203 is coupled to the processor 201, and transmits and/orreceives a radio signal. The processor 201 implements the proposedfunctions, procedures, and/or methods. In the aforementioned embodiment,an operation of the BS may be implemented by the processor 201.

An MTC device 100 includes a processor 101, a memory 102, and an RF unit103. The memory 102 is coupled to the processor 101, and stores variouspieces of information for driving the processor 101. The RF unit 103 iscoupled to the processor 101, and transmits and/or receives a radiosignal. The processor 101 implements the proposed functions, procedures,and/or methods.

The processors may include application-specific integrated circuits(ASICs), other chipsets, logic circuits, and/or data processors. Thememory may include read-only memory (ROM), random access memory (RAM),flash memory, memory cards, storage media and/or other storage devices.The RF units may include a baseband circuit for processing a radiosignal. When an embodiment is implemented in software, theabove-described schemes may be implemented using a module (process orfunction) which performs the above function. The module may be stored inthe memories and executed by the processors. The memories may bedisposed to the processors internally or externally and connected to theprocessors using a variety of well-known means.

A UE according to one disclosure of the present specification, which isan MTC device for receiving a downlink control channel, includes a radiofrequency (RF) unit to receive configuration information on a maximumnumber of PRBs which are available for a base station to transmit thedownlink control channel and configuration information on a set of PRBsfor monitoring control channel in which the MTC device needs to monitorthe downlink control channel; and a processor to monitor the downlinkcontrol channel on the PRBs according to the configuration informationon the set of PRBs for monitoring control channel, wherein when a numberof the PRBs based on the set of PRBs for monitoring control channelexceeds the maximum number of PRBs, the processor may monitor thedownlink control channel only on a set of a number of PRBs equal to orless than the maximum number of PRBs.

Here, the maximum number of PRBs for the downlink control channel may be6.

Further, the processor may monitor the downlink control channel only ona set of a number of PRBs having a relatively low PRB index, equal to orless than the maximum number of PRBs, in the set of PRBs for monitoringcontrol channel.

Further, the processor may assume that PRBs in which the downlinkcontrol channel is not monitored in the set of PRBs for monitoringcontrol channel are punctured or rate-matched.

In the above exemplary systems, although the methods have been describedon the basis of the flowcharts using a series of the steps or blocks,the present invention is not limited to the sequence of the steps, andsome of the steps may be performed at different sequences from theremaining steps or may be performed simultaneously with the remainingsteps. Furthermore, those skilled in the art will understand that thesteps shown in the flowcharts are not exclusive and may include othersteps or one or more steps of the flowcharts may be deleted withoutaffecting the scope of the present invention.

What is claimed is:
 1. A method for receiving physical downlinkchannels, the method performed by a device and comprising: performingblind decoding of downlink control information (DCI) via a firstdownlink control channel in a first subframe, which is received from acell, wherein the DCI includes scheduling information for a physicaldownlink shared channel (PDSCH), receiving, from the cell, downlink datavia the PDSCH in a second subframe based on the scheduling information,wherein a second downlink control channel is assumed to be nottransmitted in the second subframe from the cell, based on the downlinkdata being received in the second subframe.
 2. The method of claim 1,wherein bandwidth for the first downlink control channel and bandwidthfor the PDSCH are configured independent of each other.
 3. The method ofclaim 1, wherein bandwidth for the first downlink control channel andbandwidth for the PDSCH include a maximum of 6 physical resource blocks(PRBs).
 4. The method of claim 1, wherein the DCI in the first downlinkcontrol channel includes a resource allocation (RA) field which isexpressed in units of 6 PRBs.
 5. The method of claim 1, wherein thescheduling information for the PDSCH is related to cross subframescheduling such that the second subframe in which the downlink data isreceived via the PDSCH is later than the first subframe in which thedownlink data is received via the first downlink control channel.
 6. Adevice for receiving physical downlink channels, the device andcomprising: a transceiver; and a processor which controls thetransceiver and performs: performing blind decoding of downlink controlinformation (DCI) via a first downlink control channel in a firstsubframe, which is received from a cell, wherein the DCI includesscheduling information for a physical downlink shared channel (PDSCH),receiving, from the cell, downlink data via the PDSCH in a secondsubframe based on the scheduling information, wherein a second downlinkcontrol channel is assumed to be not transmitted in the second subframefrom the cell, based on the downlink data being received in the secondsubframe.
 7. The device of claim 6, wherein bandwidth for the firstdownlink control channel and bandwidth for the PDSCH are configuredindependent of each other.
 8. The device of claim 6, wherein bandwidthfor the first downlink control channel and bandwidth for the PDSCHinclude a maximum of 6 physical resource blocks (PRBs).
 9. The device ofclaim 6, wherein the DCI in the first downlink control channel includesa resource allocation (RA) field which is expressed in units of 6 PRBs.10. The method of claim 6, wherein the scheduling information for thePDSCH is related to cross subframe scheduling such that the secondsubframe in which the downlink data is received via the PDSCH is laterthan the first subframe in which the downlink data is received via thefirst downlink control channel.